Abstract
We announce the discovery of cometary activity emitting from minor planet 2018 VL10 in Dark Energy Camera images spanning from UT 2018 December 31 to UT 2019 March 3. The activity was identified by volunteers of our NASA Partner program Active Asteroids, a Zooniverse-hosted Citizen Science project designed to find previously unknown activity in known minor planets. Notably, 2018 VL10 crosses the orbits of Mars and Jupiter, and experiences close approaches of less than 0.5 au with both Earth and Jupiter. We classify 2018 VL10 as a member of the Jupiter-family comets, a group of objects especially important to understand because they hold important clues about the solar system volatile distribution, past and present.
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1. Introduction
Minor planets on orbits typically associated with comets that have not been observed to be active are known as, for example, asteroids on cometary orbits (ACOs; Licandro et al. 2006). While discerning between asteroids and comets has become increasingly challenging (see Jewitt & Hsieh 2022), ACOs may have appeared inactive upon discovery because they were inactive, or observations did not probe faint enough to detect activity. It is unsurprising, then, that ACOs may later be discovered active. Depending on their dynamical characteristics, these bodies may then be classified as belonging to a different dynamical class, e.g., Jupiter Family Comets (JFCs). Active minor planets are important to find because they harbor evidence about, for example, the solar system volatile distribution, and astrophysical processes like the Yarkovsky–O'Keefe–Radzievskii–Paddack effect (Bottke et al. 2006). It is important, then, to both identify activity in nominally asteroidal objects, as well as subsequently dynamically classifying the objects. Unlike active asteroids, JFCs are thought to originate in the Kuiper Belt and thus contain pristine primordial material that informs us about solar system formation (Levison & Duncan 1997).
2. Methods
With the goal of engaging the public in our search for active minor planets, we created the NASA Partner Active Asteroids 18 Citizen Science program (Chandler 2022; Chandler et al. 2022). We show volunteers images of known minor plants we extracted from publicly available Dark Energy Camera (DECam) data (Chandler et al. 2018) and ask if they see activity evidence (i.e., a tail or coma). Our science team examines activity candidates and searches astronomical image archives to locate more evidence of activity.
To distinguish between active asteroids and other populations we employ a metric describing Jupiter's relative influence over a body's orbit, the Tisserand parameter with respect to Jupiter, TJ (see Oldroyd et al. 2023). Objects with TJ < 3 are dynamically cometary (Levison 1996), and JFCs have 3 > TJ > 2 (Jewitt 2009).
3. Results
We identified five images of 2018 VL10 showing activity, spanning UT 2018 December 31 (heliocentric distance rH = 1.419 au, true anomaly angle f = 0°) to 2019 March 3 (rH = 1.598 au, f = 43°). Two images each from UT 2018 December 31 and 2019 February 1 (Figure 1) show strong evidence of activity in the form of a diffuse tail. A UT 2019 March 3 image (not shown) shows weak, diffuse signal in the anti-motion direction.
Figure 1. 2018 VL10 (at center) in these 32'' × 32'' DECam 150 s VR-band exposures (Prop. ID 2018B-0122, PI Rest), with north up and east left. The anti-motion (red outlined black arrow) and anti-solar (yellow arrow) directions are indicated. (a) and (b): On UT 2018 December 31 (observer A. Zenteno) a diffuse tail spans between 12 and 2 o'clock. (c) and (d): On UT 2019 February 1 (observers A. Rest, A. Zenteno) diffuse comae and/or tail(s) are seen emanating roughly toward the anti-motion and anti-solar directions.
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Notably, 2018 VL10 crosses the orbits of Mars and Jupiter and has a history of close approaches with Earth (most recently 0.479 au on UT 2019 January 9) and Jupiter (most recently UT 1997 August 18 at 0.233 au). (Close approach data retrieved UT 2023 September 24 from JPL). 2018 VL10 (semimajor axis a = 4.586 au, eccentricity e = 0.692, inclination i = 18
555, perihelion distance q = 1.413 au, aphelion distance Q = 7.759 au) has a Tisserand parameter with respect to Jupiter of TJ = 2.420, so we classify it as a JFC. Over the next thousand years 2018 VL10 undergoes deep close encounters with Jupiter that may significantly alter its orbit.
Acknowledgments
Many thanks to Arthur and Jeanie Chandler for their ongoing support.
We thank Elizabeth Baeten (Belgium) for moderating the Active Asteroids forums. We thank our NASA Citizen Scientists who examined 2018 VL10: Alex Niall (Houston, USA), Angelina A. Reese (Sequim, USA), Arttu Sainio (Järvenpää Finland), Dr. Brian Leonard Goodwin (London, UK), C. D'silva (Mumbai, India), C. J. A. Dukes (Oxford, UK), David Stefaniak (Seymour, USA), Gordon Ward (Castleford, UK), @graham_d (Hemel Hempstead, UK), Ivan A. Terentev (Petrozavodsk, Russia), José A. da Silva Campos (Portugal), Marvin W. Huddleston (Mesquite, USA), Michele T. Mazzucato (Florence, Italy), Milton K. D. Bosch MD (Napa, USA), Robert Bankowski (Sanok, Poland), Shalabh Shukla (Seattle, USA), Tiffany Shaw-Diaz (Dayton, USA), Virgilio Gonano (Udine, Italy), and Washington Kryzanowski (Montevideo, Uruguay). Thank you Superclassifiers: Angelina A. Reese (Sequim, USA), Antonio Pasqua (Catanzaro, Italy), Carl L. King (Ithaca, USA), Dan Crowson (Dardenne Prairie, USA), @EEZuidema (Driezum, Netherlands), Eric Fabrigat (Velaux, France), Henryk Krawczyk (Czeladż Poland), Robert Zach Moseley (Worcester, USA), and Thorsten Eschweiler (Übach-Palenberg, Germany). Thanks to Cliff Johnson (Zooniverse) and Marc Kuchner (NASA) for ongoing Citizen Science guidance.
This material is based upon work supported by the NSF GRFP under grant Nos. 2018258765 and 2020303693. C.O.C., H.H.H., and C.A.T. acknowledge support from NASA grant 80NSSC19K0869. W.J.O. and C.A.T. acknowledge support from NASA grant 80NSSC21K0114. This work was supported in part by NSF award 1950901. This research received support through the generosity of Eric and Wendy Schmidt by recommendation of the Schmidt Futures program. Chandler and Sedaghat acknowledge support from the DIRAC Institute in the Department of Astronomy at the University of Washington. The DIRAC Institute is supported through generous gifts from the Charles and Lisa Simonyi Fund for Arts and Sciences, and the Washington Research Foundation.
This research has made use of data and/or services provided by the International Astronomical Union's Minor Planet Center. This research uses services or data provided by the Astro Data Archive at NSF's NOIRLab and the CADC Solar System Object Information Search (Gwyn et al. 2012).
Facility: CTIO:4m (DECam) - .
Software: astrometry.net (Lang et al. 2010), JPL Horizons (Giorgini et al. 1996), SkyBot (Berthier et al. 2006).